1. Field of the Invention
The present invention relates to an initial synchronization acquiring device and method in a parallel processed DS-CDMA UWB system and a DS-CDMA UWB system's receiver using the same, and more particularly, to an initial synchronization acquiring device and method in a parallel processed DS-CDMA UWB system and a DS-CDMA UWB system's receiver using the same, which not only can simultaneously acquire an initial symbol synchronization and a frame synchronization but also can compensate a synchronization error caused by a frequency offset.
2. Description of the Related Art
The UWB (Ultra Wide-Band) system, standardization of which is being currently conducted at the IEEE (Institute of Electrical and Electronics Engineering) 802.15.3a (working group for wireless personal area network), is classified into a DS-CDMA (Direct Sequence Code Division Multiple Access) UWB system and a MB-OFDM (Multi-Band Orthogonal Frequency Division Multiplexing) UWB system. Of the two UWB systems, the DS-CDMA UWB system is currently proposed as a standard method.
The DS-CDMA UWB system transmits signals by using ultra wideband frequencies to thus seriously incur multi-path fading caused by multi-paths of a signal transmission channel, a phase offset and a signal synchronization error caused by a frequency offset generated between clocks used by a transmitter and a receiver. There have been known various methods for compensating the synchronization error. However, it is difficult to efficiently apply such existing methods to the DS-CDMA UWB system that uses an ultra-wide frequency band and performs packet data communication. The existing CDMA system designs and uses respective modules for compensating a frequency offset and tuning packet synchronization and symbol synchronization to thus have a problem in that its complexity is great.
In a data frame structure of the DS-CDMA UWB system modem, about 15 μs are assigned to a normal preamble period. In the normal preamble period, a period assigned for initial synchronization is within the range of 5 μs through 10 μs after the first preamble sequence is transmitted. Accordingly, in designing a DS-CDMA UWB receiver, it is necessary to design a searcher for acquiring initial synchronization during the preamble pattern transmission period corresponding to the 5 μs period so as to acquire initial symbol synchronization and frame synchronization. For initial synchronization, the existing IS-95 (Industry Standard-95) or WCDMA (Wideband CDMA) system transmits a pilot signal at a base station and acquires initial code synchronization from the pilot signal.
However, the UWB system needs to transmit a preamble signal instead of a pilot signal and acquire initial symbol synchronization and frame synchronization from the preamble sequence when performing communication in one piconet. Additionally, the UWB system should compensate a synchronization error caused by a frequency offset generated between clocks respectively used by a transmitter and a receiver. Accordingly, the UWB system should acquire initial synchronization within a relatively short preamble transmission period and process high-speed data to thus need a correlator and a searcher that are designed in a parallel structure.